The present invention relates to an eccentrically oscillating gear device in which an external gear is a trochoid tooth profile and an internal gear is a pinwheel.
An eccentrically oscillating gear device is used in a reducer for driving an arm member of a robot provided to a joint portion of an industrial robot, for example. The following Patent Document 1 discloses an eccentrically oscillating gear device in which an external gear comprises a peritrochoid tooth profile and an internal gear comprises a pinwheel. In this eccentrically oscillating gear device, as shown in FIGS. 4(a), (b), by cutting out the tip portions of the respective tooth tops 51a of the external gear 51, the tip portions are avoided from coming into contact with the inner-diameter portions of the main body of the internal gear member having circular grooves in which pins 52 are inserted, and the time for which the pins 52 located at a side of the internal gear 53 which does not contribute to the transmission of torque is forcedly rotated on its axis is reduced to thereby reduce the internal heat generation, so that breakdown caused by burn-in can be avoided.
When the tip portions of the tooth tops 51a of the external gear 51 as described above are cut out, as shown at the lower portion of FIG. 4(a) and FIG. 4(b), the pins 52 idle at the 180° counter position in the eccentric direction, and thus the pins 52 are easily inclined or easily drop off from pin grooves 52a. When such a situation occurs, the external gear 51 having the peritrochoid tooth profile bite at the pins 52, so that abnormal noise occurs or the pin grooves 52a are deformed. Furthermore, the output of a spur gearing may be locked.
In order to solve the above problem, as shown in FIGS. 5, 6, it is necessary that a pin press ring 55 is disposed between the external gears 51 and 51 to constrain the pins 52 (suppress inclination of the pins) (FIG. 5), or it is also necessary that a pin press ring 56 is disposed between the external gear 51 and a bearing 58 and another pin press ring 57 is disposed between the external gear and a bearing 59 (FIG. 6) (for example, see Japanese Patent Application Nos. JP-A-02-261943 and JP-A-05-180278).
However, when pin press members such as the pin press rings 55 to 57 shown in FIGS. 5 and 6 are used, the number of parts is increased, and also the device is designed to be large in the axial direction P, so that the degree of freedom of design is lost.